Brostaígí - - hurry (to two or more people);
brostaigh - - hurry (to one person)

There are two groups of verbs, briathra, in Irish: An Chéad Réimniú - - The First Conjugation; and An Dara Réimniú - - The Second Conjugation. There are eleven irregular verbs, na briathra neamhrialta, which are not too irregular as they mostly follow the rules of An Chéad Réimniú.

An Chéad Réimniú has mostly verbs of one syllable: tóg -- take; fan - - wait, stay; múch - - quench; suigh - - sit; lig - - allow, let; dún - - close; éist - - listen. There are some verbs of more than one syllable such as taispeáin - - show and the ever-increasing --áil verbs! Sábháil - - save; spáráil - - spare; and so on (using the English verb with the - -áil ending to make an Irish verb!!)

An Dara Réimniú has verbs of more than one syllable, many of them ending in -aigh or -igh like brostaigh - - hurry; ceannaigh - - buy; éirigh - - get up; deisigh - - repair.

Na Briathra Neamhrialta are déan - - do, make; bí - - be; téigh - - go; faigh - - get; tar - - come; abair - - say; beir - - catch, bring; clois - - hear; feic - - see; ith - - eat; tabhair - - give.
N.B. Use éist - - listen instead of clois as a command and féach or breathnaigh or amharc- - look instead of feic.
I believe these verbs are irregular because they are the most frequently used and retain old stems.